1. Field of Invention
This invention relates to a semiconductor integrated circuit including an anti-fuse formed on a surface of a semiconductor substrate and a method for manufacturing the same.
2. Description of Related Art
Anti-fuses have been proposed that can be changed or programmed from a non-conductive state to a conductive state by applying a writing voltage, in a semiconductor integrated circuit. By programming specific anti-fuses to a conductive state, an internal circuit of the integrated circuit may be configured in a desirable operational state.
U.S. Pat. No. 5,973,380 discloses an anti-fuse including a pair of n+ regions closely spaced in a p-type substrate. The anti-fuse is converted to a state that conducts current from a state that blocks current flow by applying a breakdown voltage between the n+ regions.
However, an initial failure, in which leakage current flows before the anti-fuse is programmed, is likely to occur in the anti-fuse disclosed in this Patent.
U.S. Pat. No. 5,019,878 discloses a programmable device formed from a silicided MOS transistor. The device is programmable by applying a programming voltage, which is greater than or equal to the source-drain breakdown voltage, between the drain region and source region to form a conductive filament in the channel region that couples the drain region and the source region.
However, programming of this device requires applying a high voltage between the drain and source regions, and a suitable voltage to the gate electrode. Accordingly, a complicated programming circuit, or a writing circuit, that supplies the suitable voltage to the gate electrode in addition to the high voltage between the drain and source region, is required.
The assignee of this application already disclosed an anti-fuse device in U.S. patent application Ser. No. 10/076,652 (now U.S. Pat. No. 6,608,355), which is incorporated herein by reference in its entirety. In this prior application, it was proposed to decrease the breakdown voltage of a MOS transistor, which is used as an anti-fuse, by controlling the dopant concentration in the channel region. The decreased breakdown voltage decreases the required writing voltage and renders unnecessary the supply of a suitable voltage to the gate electrode during application of the writing voltage.